WITS WATER FILTER, Arsenic Removal Matrix

A Simple, Low Cost, And Effective Arsenic Removal Filter

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Preliminary
(The Useful Bit)

Introduction
(The Technical Bit)

Chemistry and general considerations
(The Science Bit)

Tests and performance
(The Boring Bit)

Operation and maintenance
(The Interesting Bit)

Future outlook
(The Last Bit)

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Tests and performance (The Boring Bit)

The WITS filters were tested only with real groundwater contaminated with arsenic and other species. From the inception of our research, we realized that the fastest way to test for filter efficacy was to use real groundwater containing varied concentrations of arsenic, iron, other inorganic species and water quality parameters in Bangladesh. Thus we selected 6 tube wells in 6 different households where WITS filters were installed. All the filters removed arsenic to less than10 µg/L from an input range of 32–2423 µg/L As(Total). All filters removed soluble Fe below 0.26 mg/L, even from the highest input Fe of 21 mg/L. It is important to mention that we have identified arsenicosis patients in the last 3 locations where arsenic concentrations are above the suggested 300 µg/L.

These experimental filters continue to provide clean potable water for the households. Due to the combination with the material ARM, the other components of the filters and the optimum arrangement of these materials, the WITS filter removes arsenic, iron, manganese and many other inorganic species to a potable water.

Our oldest filter has been working for 5 years now, and with regular maintenance has had no breakthrough. The filter can work at 60 L/hour flow rate without breakthrough. However, due to the unknown water chemistry and varied As(total) in groundwater, we have fixed the flow rate to 20–30 L/hour to ensure long-term use and effluent As(total) below 30 µg/L. In contrast, blank filters breakthrough occurs at 88 Litres groundwater. These experiments also demonstrated that plain sand filter broke through the MCL almost instantaneously. A low iron (1.0 mg/L) containing groundwater was selected for this study to ensure HFO precipitate from this iron would not bias the results by co-precipitation and complexation of arsenic species.

Several NGOs have installed WITS filters in many arsenic affected areas of Bangladesh. One such most affected area is Hajigong, where 165 WITS filters were installed to supply water for 300 arsenicosis patients and 3,000 family members. The results published show As (total)in filtered water was<2µg/L (70% samples), <10µg/L (20% samples), <30 µg/L (10% samples), and none above 30 µg/L from the influent As(total) 600–700 µg/L with at least 50% in the form of more toxic As(III). The study also found no change in flow rate and no maintenance required for 12 months.